install of thermostatic shower controls all hot water!

[crispibits]

Boiler = baxi 105e gas combi
Shower unit = Bristan Cardinal thermostatic
'Good' mains water pressure (don't know what bar or anything like that I'm afraid).

I just installed a thermostatic shower, and now all our hot water (from all taps) comes out warm, not hot! If I isolate either hot or cold supply to the shower, all tap hot water comes out nice and hot.

I have installed flow limiters as per Bristan instructions for a combi boiler, and followed all other instructions that came with the unit.

The shower is a replacement for an old non-thermostatic manual shower, and no other changes have been made to the pipework.
Does anyone have ideas why this might be? I'm wondering if somehow cold water is 'mixing back'? I've searched these forums but found no similar circumstances. The only thing I can think is that a non-return valve might be needed, but haven't found anything in instructions about needing them, and hadn't come across them before googling today...
Please let me know if I need to give any more information?
Thanks,
Crispin

 

[swbjackson]

As it stops happening when you isolate the shower it's got to be back flow. I would contact Bristan and ask as there may be a problem with the new shower. It's worth fitting a check valve anyway.

 

[crispibits]

Thanks - I suspected that may the case - just wanted to 'tap' (geddit?) the knowledge of you lot to see if there was anything I could do before Bristan open again on Tuesday.
Also - as per usual, after I posted I came across the following topic:
//www.diynot.com/forums/viewtopic.php?t=110681
Sounds similar.
1/ Would there be any reason why I *shouldn't* fit a check valve to the hot feed - I can't imagine it doing any harm, but then I'm not an expert, hence asking here!
2/ Should I fit check valves to both hot and cold?

Thanks in advance, as ever most helpful!

 

[swbjackson]

It's possible for the backflow to go either way depending on usage so you may as well fit them to both to prevent future problems.

 

[crispibits]

Just thought I'd follow up on this. Looks like the shower unit should have check valves in the water supply elbows, but they seem to be missing. Although it took ages to get through to Bristan, once there they were very helpful, and they're posting out some for me. Thanks for the advice - helped me talk sense when talking to Bristan

 

[crispibits]

Received check valves from Bristan next day - all fitted and works perfectly. Credit to them for quick supply, and to swbjackson for confirming my suspicions, thanks!